U.K. crisp (chips to us North Americans) lovers upset that one of the country’s biggest snack-food brands doesn’t use recyclable packaging have found a creative way to express their frustration.

Several people have tweeted photos of them dropping Walkers chip bags, addressed to the company’s consumer services department in Leicester, in mailboxes.

It’s part of a campaign to force Walkers and other companies to start using more environmentally friendly packaging than the layers of aluminum and plastic that make up most chip bags. “As a nation, the U.K. alone consumes approximately six billion packets a year,” wrote Gerraint Ashcroft, who started the campaign on petition site 38 Degrees.

But the country’s postal service has asked the campaigners to put the bags in envelopes before sending them off. “Crisp packets can’t go through the machines, they are not normal mail items, therefore my hardworking colleagues need to manually sort them, which adds to time,” a Royal Mail spokesperson told BBC News.

Some on Twitter also criticized the protest method, saying that it would make more sense to boycott Walkers instead.

38 Degrees said in a tweet that it was encouraging people to mail back bags they already had, not to buy more chips.

Walkers’ parent company, PepsiCo, is one of a number of corporations that have agreed to make all of their plastic packaging recyclable, compostable or reusable by 2025 as part of a U.K. initiative to reduce waste. The food-industry giant recently won an award, along with a company that makes bio-resins, for its work on a new compostable chip bag.

In most places, chip packages aren’t recyclable, because the layers of plastic and aluminum can’t be easily separated. But as of this past summer, British Columbians can now drop off their empty Lay’s bags at certain Recycle B.C. depots, along with other items that traditionally end up in the trash, like cheese-slice wrappers and hand-soap refill pouches.

Recycle B.C., a non-profit that manages residential recycling in many parts of the province, said in a May news release that it was working with a company to find a way to recycle these sorts of plastics. It said any materials that can’t be recycled will be turned into fuel.